Texas police are defending their decision to arrest an Iraq war veteran who is charged with manslaughter after a young daughter died in his hot pickup truck and a second daughter was hospitalized, although his family maintains his innocence.

"Nobody blames Russel, it wasn't a thing that he did. It just happened," Marguerite Youngblood, the suspect's mother, told ABC News affiliate KLTV.

Russel Lindstrom, 33, of Flint, Texas, was charged on Wednesday with manslaughter and injury to a child, said Krista Caulkins, an administrative assistant for the Smith County Sheriff's Office.

Despite his mother's belief in his innocence, Caulkins told ABC News that the sheriff's office does have reason to suspect Lindstrom of foul play.

"An in-depth investigation occurred before he was arrested," Caulkins said.

"With an investigation such as this not all the facts are released. There were other statements he [Lindstrom] made when he was interviewed by [the sheriff’s office] on June 11 and evidence gathered from an evidentiary search warrant issued on Jun 11."

Lindstrom, who according to his family is a military veteran who served in Iraq, is being held on $200,000 bail.

"He has invoked his Fifth Amendment rights and asked for an attorney," Caulkins said.

Bella, 4, and her sister Zoey, 3, were found by their father locked and unresponsive in his pickup truck at their home on the afternoon of June 11.

The girls were supposed to be napping, but were not in their bedroom when Lindstrom went to check on them, he told KLTV.

"The bedroom is at the front of the house," Youngblood said to KLTV. "That is how they could easily enough get out the door and get into the vehicle with him [Lindstrom] being in the back of the house."

When Lindstrom found his daughters locked in his truck he unlocked the vehicle and took them out. It is unclear how long the girls were inside.

"The children locked themselves in the vehicle, but Lindstrom was able to get them out because he had the keys," Caulkins said.

Bella was taken to a hospital where she died. Her sister, Zoey, was treated at the home and taken to the hospital for overnight observation, according to a statement written by Smith County Sheriff Larry Smith.

Investigators ordered an autopsy for the 4-year old and have taken the pickup truck to a crime lab.

Police are not pursuing any other suspects because Lindstrom was home alone with his daughters at the time of the incident, according to Caulkins.

Youngblood has been seeking donations online to pay for an attorney for Lindstrom, according to a page she created on the website Go Fund Me.

The case against Lindstrom comes in the wake of Georgia dad Ross Harris' arrest and charge with felony murder after leaving his son in a minivan on a hot day, killing him. Harris' family has defended him against the murder charge.

Police have said that Harris looked up stories on the internet about children dying in hot cars and spent part of the day his son died sexting with strange women.